The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An engine combusts an air/fuel mixture to generate drive torque for a vehicle. The air is drawn into the engine through a throttle valve and an intake manifold. The fuel is provided by one or more fuel injectors. The air/fuel mixture is combusted within one or more cylinders of the engine. Combustion of the air/fuel mixture may be initiated by, for example, compression provided by a piston and/or spark provided by a spark plug. Combustion of the air/fuel mixture produces exhaust gas. The exhaust gas is expelled from the cylinders to an exhaust system.
The exhaust system includes a catalyst, such as a three-way catalyst, that reacts with the exhaust gas to reduce emissions. “Three-way” refers to the three emissions that a catalytic converter reduces, including carbon monoxide (CO), unburned hydrocarbons (HCs) and nitrogen oxide (NOx). The catalyst, however, may be unable to react when the temperature of the catalyst is less than a light-off temperature. Accordingly, the catalyst's reaction capability may be limited upon engine startup (e.g., key ON) when the catalyst temperature is less than the light-off temperature.
An engine control module (ECM) controls the torque output of the engine. For example only, the ECM controls the torque output of the engine based on driver inputs and/or other inputs. The ECM also controls various engine parameters to warm the catalyst when the catalyst temperature is less than the light-off temperature. For example only, the ECM may retard the spark timing to provide hydrocarbons in the exhaust gas. Oxidation of hydrocarbons in the exhaust system produces heat, which warms the catalyst.
The amount of heat produced via hydrocarbon oxidation is limited by the amount of oxygen in the exhaust system. A secondary air pump may be mechanically coupled to a cylinder head to provide air directly to the cylinder head. The air delivered by the secondary air pump increases the amount of oxygen in the exhaust system and, therefore, the secondary air pump increases hydrocarbon oxidation capability. The ECM may control operation of the secondary air pump to control oxidation of hydrocarbons in the exhaust system and warm the catalyst.